Carpets are widely used in office buildings, housing, and the like, as a floor material which has a high thermal insulation effect and a high sound insulation effect, provides easy conveyance and installation, and is partially replaceable. Carpets are made of various fiber materials, and have a variety of colors and textures, so that they are an important interior item to enrich the living.
The types of carpets are classified into, for example, a tufted carpet, a Wilton carpet, a bonded carpet, a knitted carpet, and a needle punched carpet according to the difference of the manufacturing methods thereof. Among the types of carpets, the tufted carpet is obtained by penetrating, with sewing machine needles, a pile yarn of nylon, wool, polyester, polypropylene, acryl, or the like into a backing fabric (woven backing fabric, spunbonded fabric) to continuously make loop or cut piles. The specification of the tufted carpet is determined by the number of penetrations (gauge) in the width direction of the carpet, the number of penetrations in the length direction (stitch), and the length of a pile (pile height).
The tufted carpet is produced by a tufting machine. In the tufting machine, needles are arranged with the same intervals in the width direction and a pile yarn is penetrated into a backing fabric with these needles. The interval among the needles is called a gauge. For example, a 1/10 gauge (G) tufting machine has 10 needles in 1 inch in the width direction, i.e. about 1600 needles in a width of 4 m. A yarn is put through a needle and the yarn is penetrated into a backing fabric fed at a constant speed to form a pile for making an uncolored original tufted carpet. The made original carpet is subjected to a dyeing process.
A common method for dyeing a tufted carpet includes a continuous dyeing method of continuously dyeing a long original tufted carpet while running it in the longitudinal direction (for example, see Patent Document 1), a wince dyeing method of connecting a certain length of a tufted original carpet in a rope shape within a dyeing machine, and dyeing the original carpet while turning it around, and a print dyeing method of dyeing an original carpet with a pattern dyeing machine of screen printing, jet printing, or the like. The print dyeing method is excellent in attainability of expression of a fine pattern, but has slow processing speed and has high production costs. Therefore, the print dyeing method is rarely used except for producing a luxury product. The wince dyeing method has lower production costs than the print dyeing method, but cannot attain expression of a fine pattern and is not suitable for mass production. On the other hand, the continuous dyeing method has high processing speed and has low production costs, and therefore, is widely and commonly used. However, the continuous dyeing method is, basically, a method aiming at dyeing for even and single color expression so that color difference does not appear in the width direction and the length direction. Therefore, in the present circumstances, it is not considered to attain expression of a pattern by gradation, or mixture of a plurality of colors by the continuous dyeing method.